Wake Shield Facility
The WSF was deployed in the wake of the Space Shuttle at an orbital altitude of over 300 kilometers (186 mi), within the thermosphere, where the atmosphere is exceedingly tenuous. The forward edge of the WSF disk redirected atmospheric and other particles around the sides, leaving an "ultra-vacuum" in its wake. The resulting vacuum was used to study epitaxial film growth.
The WSF has flown into space three times, on board shuttle flights STS-60, STS-69 and STS-80. During STS-60, some hardware issues were experienced, and, as a result, the WSF was only deployed at the end of the shuttle's robotic arm. During the later missions, the WSF was deployed as a free-flying platform in the wake of the shuttle.
These flights proved the vacuum wake concept, and realized the space epitaxy concept by growing the first-ever crystalline semiconductor thin films in the vacuum of space. These included gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) depositions. These experiments have been used to develop better photocells and thin films. Among the potential resulting applications are artificial retinas made from tiny ceramic detectors.
Pre-flight calculations suggested that the pressure on the wake side could be decreased by some 6 orders of magnitude over the ambient pressure in low Earth orbit (from 10−8 to 10−14 Torr). Analysis of the pressure and temperature data gathered from the two flights concluded that the decrease was some 2 orders of magnitude (4 orders of magnitude less than expected).
The Wake Shield is sponsored by the Space Processing Division in NASA's Office of Life and Microgravity Sciences and Applications. Wake Shield was designed, built and is operated by the Center for Advanced Materials (formerly Space Vacuum Epitaxy Center) at the University of Houston—a NASA Commercial Space Center—in conjunction with its industrial partner, Space Industries, Inc., also in Houston.
- Advanced thin-film materials processing in the ultra-vacuum of space - Acta Astronautica, Volume 48, Issues 2–3, 2 January 2001, Pages 115–120
- Photoluminescence of GaAs grown by metallorganic molecular beam epitaxy in space ultra-vacuum – Journal of Crystal Growth, Volume 209, Issues 2–3, February 2000, Pages 435–439
- Wake vacuum measurement and analysis for the wake shield facility free flying platform - Vacuum, Volume 64, Issue 2, 27 November 2001, Pages 119–144